I had a science teacher that started each new unit
with a science trick (magic tricks using scientific principles to make them
work). He wouldn't give us the secret of how he made the trick work
-- it would always be a 'bonus question' on the quiz. If you understood
the science unit you could figure out the trick.

I remember being completely enthralled by the tricks (and completely
motivated to learn the science just so I could figure out how the trick
worked).